BIO 205 – Microbiology Chapters 8, 9, end of Ch. 3

BIO 205 – Microbiology

Chapters 8, 9, end of Ch. 3

Chapter 8 - Growth of Microorganisms

Key words / concepts

•doubling / generation time•binary fission•the growth phases of a population

• lag, exponential, stationary, death•colony•biofilm•trance elements vs. growth factors•temperature “requirements”•oxygen requirements•pH and salt “requirements”•bacterial counts•dilution plating / spread plate technique

How do most bacteria replicate?

Some do it a bit different . . .

Listeria monocytogenes

Generation time

Growth Phase

Continuous culture in a chemostat

Types of Growth

Streak plate technique

Biofilms

Biofilms and quorum sensing

Biofilms

Microbial nutrition

Microbial nutrition

Trace elements

Growth factors

Nutritional classes of microorganisms

carbon from CO2

Defined media Produced from pure chemicals

Complex media Extracts of natural sources

▪ Beef, blood, milk, protein, yeast, soybeans

▪ Precise composition not known Selective media

Contents select for specific microorganism

Differential media Identification of microorganisms

Defined media none

Complex media Nutrient agar Mueller Hinton agar - antibiotic testing

Selective media EMB - inhibit growth of Gram positive bacteria MacConkey - inhibit growth of Gram positive bacteria Mannitol salt - high salt (staph will grow)

Differential media Sheep Blood agar - hemolysis EMB - lactose and/or sucrose fermentation - fecal

coliforms MacConkey - lactose fermentation Mannitol Salt - mannitol fermentation - pathogenic staph Enterotube - rapid ID of enteric bacteria (15 tests in 1) Synder - dental caries susceptibility - acid producers in

saliva

How temperature affects growth

Oxygen requirements

aerobe

anaerobe

obligate / strict

facultative

microaerophile

aerotolerant

Oxygen culturing conditions

• Culturing– Shaking machines

• Increase oxygen in the media

– Candle jars• Not anaerobic but

reduces available oxygen

– Anaerobic chambers• All oxygen is replaced

with other gas Figure 3.25

How do we visualize oxygen requirements in the lab? (stab vs. broth)

pH and salt and bacterial growth

halophilic

How do you know how much bacteria there is?

How do you know how much bacteria there is? Hemocytometer

Viable count = dilutions and plating

Pour vs. spread plate technique

Plate count

A little math for you!

plate 1 ml of bacteria onto agar plate

5348 672 126 28

Summary - Growth of Microorganisms

Chapter 9 - Controlling Microorganisms

How we used to protect ourselves from microbes

Sterilization

Disinfection / sanitizing

Decontamination

Antiseptics / antisepsis

Bactericide vs. Bacteriostatic

Methods of Physical Control

Heat

• moist heat

• dry heat

cold

Preserving cultures

• Cold storage– Short-term: refrigeration slows growth

• Must continually transfer

– Long-term: freezing• Add substance to reduce freeze-killing

– Glycerol, skim milk, dimethyl sulfoxide (DMSO)

– Lyophilization• Long term—freeze drying• Frozen and dried under vacuum• probiotics

Methods of Physical Control

autoclave incineration

Sterilization

Eliminating all microorganismsCulture media must be sterilizedHeat sterilization

Moist heat▪ Autoclave▪ 121oC for 20 minutes

Dry heat▪ 170oC for 90 minutes

Figure 3.20

Methods of Physical Control

pasteurization

Thermal Death What?

Thermal Death Time

Thermal Death Point

Methods of Physical Control

Radiation

• nonionizing (UV)

• ionizing

Methods of Physical Control

Methods of Physical Control

Filtration

Lyophilization

Methods of Chemical Control

germicides - activity classified as

high intermediate low

Assignment for next week:What do you use (at home or work)? How does it work?

Methods of Chemical Control

•Phenols / phenolics

•Alcohol

Methods of Chemical Control

• Halogens

• Hydrogen Peroxide

Methods of Chemical Control

•Heavy metals

• Surfactants / detergents

Testing germicides

we will do Nov. 9

Testing germicides

Less light = higher concentration of toxin = less bacteria still alive

Highest ConcentrationOf toxin

Preserving Food

Preserving Food

Fig. 1. Flow diagram of the main routes of spore contamination into foods. A circled Sp indicates possible environments for formation of endospores (sporulation).